If ever a site dictated a question that must be asked in a presidential debate, it is Denver. Two of the worst mass shootings in the nation’s history happened in its suburbs, at Columbine High School in 1999 and at a movie theater in Aurora this summer. The shootings combined killed 27 people and injured 81.

Moderator Jim Lehrer will spend half of Wednesday’s 90-minute debate between President Obama and Mitt Romney on the economy. That is understandable. But somewhere in the remaining half dedicated to “health care,” “the role of government,” and “governing,” he must ask about the obvious issue: guns.

The question was no better stated than by Tom Mauser, whose son Daniel was one of the students killed at Columbine. Now a gun control activist, he said in a telephone interview that he wrote Lehrer to urge him to grill Obama and Romney on firearms laws. I asked Mauser what he would ask the candidates. He replied: “How many deaths are enough for either of you to become concerned?”

He deserves an answer. Mere hours after our conversation on Thursday, a man who reportedly was fired by a Minneapolis sign-making business returned to the premises and shot company founder Reuven Rahamim dead. The shooter killed four others, including a UPS driver, and wounded three others before killing himself.

In standard political lament, Governor Mark Dayton said, “I deplore this senseless violence. There is no place for it anywhere in Minnesota.” This was yet another deploring of tragedy that came without any commitment to fight for gun control.

If there is no place for senseless violence, then Lehrer should put Obama and Romney on the hot seat as to why Aurora and subsequent mass shootings, such as the one at a Sikh temple in Wisconsin, changed nothing. The Democrats say in their party platform that they want to reinstate the assault weapons ban, close the gun-show loophole, and strengthen the federal background-check system. That platform says, “We believe in an honest, open national conversation about firearms.”

But Obama has kept his mouth closed ever since the headlines of Aurora died down.

Meanwhile, the Republican Party platform opposes gun control limits even for the capacity of clips and magazines. In Minneapolis, police found 10,000 rounds of ammunition in the apartment of the alleged assailant. The Aurora shooter legally purchased online 6,000 rounds and a 100-round drum magazine. Romney recently told the National Rifle Association that he opposes reinstating the assault weapons ban and supports letting right-to-carry permit holders carry guns across state lines. “I do not support any additional laws to restrict the right to keep and bear arms,” he said.

Meanwhile, Smith and Wesson and Sturm, Ruger and Company are reporting record gun sales. In an August press release, Ruger CEO Mike Fifer boasted, “Last year, Ruger became the first commercial firearms company to produce 1 million firearms in one year, and we were incredibly excited and proud to reach that milestone. It took us nearly all of 2011 to build 1 million firearms, but in 2012 we accomplished it on Aug. 15th.”

Federal background checks, a strong indicator of gun sales, have nearly doubled since 2005. That distresses Mauser, who fears it will take a catastrophe far worse than Aurora, one with many more victims, before politicians free themselves from the grip of the NRA.

“There’s a whole lot of us don’t want to be armed, but the political environment tells us that we’re fools for not buying guns,” said Mauser, a manager for the Colorado Department of Transportation. “But it’s time to look around. The NRA says we need more guns in more places and more kinds of guns any time, any place, and we’d be the safest nation on earth. But we are the most violent (among developed nations). What politician is going to have the courage to challenge that vision of our country?”

Lehrer needs to ask that question, so America can finally get an answer.